Evolution of radio access schemes and radio networks of cellular mobile communication (hereinafter, referred to as “Long Term Evolution (LTE) or “Evolved Universal Terrestrial Radio Access (EUTRA)) has been standardized in 3rd Generation Partnership Project (3GPP). In LTE, an Orthogonal Frequency Division Multiplexing (OFDM) scheme which is multi-carrier transmission is used as a communication scheme of radio network communication from a base station device to a mobile station device (a downlink: referred to as a DL). In LTE, a Single Carrier-Frequency Division Multiple Access (SC-FDMA) scheme which is single carrier transmission is used as a communication scheme of radio network communication from a mobile station device to a base station device (an uplink: referred to as an UL). In LTE, a Discrete Fourier Transform-Spread OFDM (DFT-Spread OFDM) scheme is used as the SC-FDMA scheme.
With development of LTE, LTE-Advanced (LTE-A) to which new technologies are applied has been examined. In LTE-A, supporting at least the same channel configuration as that of LTE has been examined. A channel means a medium used to transmit a signal. A channel used in the physical layer is referred to as a physical channel and a channel used in the Medium Access Control (MAC) layer is referred to as a logical channel. The types of physical channel include a Physical Downlink Shared CHannel (PDSCH) used to transmit and receive data and control information of the downlink, a Physical Downlink Control CHannel (PDCCH) used to transmit and receive control information of the downlink, a Physical Uplink Shared CHannel (PUSCH) used to transmit and receive data and control information of the uplink, a Physical Uplink Control CHannel (PUCCH) used to transmit and receive control information, a Synchronization CHannel (SCH) used to establish downlink synchronization, a Physical Random Access CHannel (PRACH) used to establish uplink synchronization, and a Physical Broadcast CHannel (PBCH) used to transmit system information of the downlink. A mobile station device or a base station device maps a signal generated from control information, data, or the like to each physical channel to transmit the signal. Data transmitted with the physical downlink shared channel or the physical uplink shared channel is referred to as a transport block.
Control information mapped in a physical uplink control channel is referred to as uplink control information (UCI). The uplink control information is control information (reception confirmation acknowledgement: ACK/NACK) indicating positive acknowledgement (ACK) or negative acknowledgement (NACK) to data received and mapped in Physical Downlink Shared Channel, control information (Scheduling Request: SR) indicating a request to assign uplink resources, or control information (Channel Quality Indicator: CQI) indicating reception quality (also referred to as channel quality) of the downlink.
<Cooperative Communication>
In LTE-A, inter-cell cooperative communication (Cooperative Multipoint: CoMP communication) in which communication is performed cooperatively between neighboring cells has been examined in order to reduce or suppress interference to a mobile station device at a cell end region or in order to increase reception signal power. For example, a form in which a base station device performs communication using any one frequency band is referred to as a “cell.” For example, a method (also referred to as Joint Processing or Joint Transmission) in which weighting signal processing (precoding process) different in a plurality of cells is applied to signals and a plurality of base station devices cooperate with each other to transmit the signal to the same mobile station device has been examined as the inter-cell cooperative communication. In this method, a ratio of signal power to interference noise power of a mobile station device can be improved, and thus reception characteristics of the mobile station device can be improved. For example, a method (Coordinated Scheduling: CS) of performing scheduling on a mobile station device cooperatively between a plurality of cells has been examined as the inter-cell cooperative communication. In this method, the ratio of signal power to interference noise power of the mobile station device can be improved. For example, a method (Coordinated beamforming: CB) of transmitting a signal to a mobile station device by applying beamforming cooperatively between a plurality of cells has been examined as the inter-cell cooperative communication. In this method, a ratio of signal power to interference noise power of the mobile station device can be improved. For example, a method (Blanking, Muting) in which only one cell transmits a signal using a predetermined resource and the other cell does not transmit a signal using the predetermined source has been examined as the inter-cell cooperative communication. In this method, a ratio of signal power to interference noise power of the mobile station device can be improved.
In a plurality of cells used in the cooperative communication, different cells may be configured by different base station devices, different cells may be configured by different Remote Radio Heads (RRHs: outdoor type radio network units smaller than a base station device in size, also referred to as a Remote Radio Unit (RRU)) managed by the same base station device, different cells may be configured by a base station device and an RRH managed by the base station device, or different cells may be configured by a base station device and an RRH managed by a base station device different from the base station device.
A base station device with a broad coverage is generally referred to as a macro base station device. A base station device with a narrow coverage is generally referred to as a pico base station device or a femto base station device. Generally operating the RRH in an area with a coverage narrower than the macro base station device has been examined. Development as in a communication system configured by macro base station devices and RRHs and configured such that coverages supported by the macro base station devices include some or all of the coverages supported by the RRHs is referred to as heterogeneous network development. In a communication system of the heterogeneous network development, a method in which the macro base station devices and the RRHs cooperate with each other to transmit a signal to mobile station devices located within the mutually overlapping coverages has been examined. Here, the RRHs are managed by the macro base station devices such that transmission and reception is controlled. The macro base station devices and the RRHs are connected by wired lines such as optical fibers or a wireless lines using relay technologies. Thus, when some or all of the macro base station devices and the RRHs perform the cooperative communication using the same radio network resources, it is possible to improve comprehensive frequency efficiency (transmission capacity) within areas of the coverages constructed by the macro base station devices.
When a mobile station device is located near the macro base station device or the RRH, single cell communication with the macro base station device or the RRH can be performed. That is, a certain mobile station device performs communication with the macro base station device or the RRH to transmit or receive a signal without using the cooperative communication. For example, the macro base station device receives a signal of the uplink from a mobile station device located to be close to the macro base station device itself. For example, the RRH receives a signal of the uplink from a mobile station device located to be close to the RRH itself. When the mobile station device is located near an end (cell edge) of the coverage constructed by the RRH, countermeasures against the same channel interference from the macro base station device are necessary. A method of reducing or suppressing interference to a mobile station device in a cell edge region by using a CoMP scheme in which neighboring base station devices cooperate to each other as multi-cell communication (cooperative communication) with the macro base station device and the RRH has been examined.
The fact that a mobile station device receives signals transmitted from both of a macro base station device and an RRH using cooperative communication with a downlink and transmits a signal to either of the macro base station device and the RRH in an appropriate form with an uplink has been examined. For example, the mobile station device transmits an uplink signal with transmission power appropriate for reception of a signal to the macro base station device. For example, the mobile station device transmits an uplink signal with transmission power appropriate for reception of a signal by the RRH. Thus, it is possible to reduce unnecessary interference in an uplink and improve frequency efficiency.
The mobile station device needs to acquire control information indicating a modulation scheme used for a data signal, a coding rate, a spatial multiplexing number, a transmission power adjustment value, assignment of resources, or the like in regard to a data signal reception process. In LTE-A, introducing a new control channel transmitting control information regarding a data signal has been examined (see NPL 1). For example, improving the capacity of all of the control channels has been examined. For example, supporting interference coordination in a frequency domain in the new control channel has been examined. For example, supporting spatial multiplexing in the new control channel has been examined. For example, supporting beamforming in the new control channel has been examined. For example, supporting diversity in the new control channel has been examined. For example, using the new control channel with a new type of carrier has been examined. For example, performing no transmission of a reference signal common to all of the mobile station devices in a cell in the new type of carrier has been examined. For example, reducing transmission frequency of the reference signal common to the mobile station devices in a cell further than that in the related art in the new type of carrier has been examined. For example, demodulating a signal such as control information using a reference signal unique to a mobile station device in the new type of carrier has been examined.
For example, applying cooperative communication or transmission of a plurality of antennas to the new control channel as application of beamforming has been examined. Specifically, the fact that a plurality of base station devices and a plurality of RRHs corresponding to LTE-A apply a precoding process to a signal of the new control channel and also apply the same precoding process to a reference signal (RS) for demodulating the signal of the new control channel has been examined. Specifically, the fact that a plurality of base station devices and a plurality of RRHs corresponding to LTE-A map the signals and the RSs of the new control channel to which the same precoding process is applied to regions of resources in which the PDSCH is mapped in LTE and transmit the signal and the RSs has been examined. The fact that a mobile station device corresponding to LTE-A demodulates the signal of the new control channel subjected to the same precoding process using the RS which is the received RS and is subjected to the precoding process and acquires control information has been examined. In this method, it is not necessary to exchange information regarding the precoding process applied to the signal of the new control channel between the base station device and the mobile station device.
For example, as application of the diversity, a method of configuring the signal of the new control channel using a resource distant from a frequency domain and obtaining the advantageous effects of frequency diversity has been examined. On the other hand, when the beamforming is applied to the new control channel, a method of configuring the signal of the new control channel using a resource not distant from a frequency domain has been examined.
For example, as the support of the spatial multiplexing, it has been examined that Multi User-Multi Input Multi Output (MU-MIMO) of multiplexing control channels for different mobile station devices with the same resource is applied. Specifically, it has been examined that the base station device transmits reference signals orthogonal between different mobile station devices and performs spatial multiplexing on signals of new different control channels to common resources to transmit the signals. For example, the spatial multiplexing on the signals of the new different control channels is realized by applying beamforming (precoding process) suitable for the signals of the new different control channels.